Molecular genetics is a branch of genetics that focuses on the function of genes, and their alleles, at the molecular level, as well as the physiological effects associated with the differences in the alleles.
There are three main base coat colors in horses: Black, Bay, and Chestnut. These base phenotypes are produced by the interaction of two main genes: the Agouti (A) Gene and the Extension (E) Gene. The Extension (E) Gene dictates whether black or a reddish-yellow pigment is produced, and the Agouti (A) gene dictates the extent to which the black pigment is expressed.
Mutations in the DNA sequences for these genes cause the production of different alleles. Mutations in the Agouti (A) Gene result in an allele that codes for a non-functional protein to be produced, and allows for the partial expression of the black pigment. Mutations in the Extension (E) Gene result in an allele that codes for a non-functional hormone receptor, that prevents black pigment from being produced and allows for a reddish-yellow pigment to be dominant.
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